This invention relates to a monitor for monitoring the clearance between the blades and shearbar of a cutting tool, and in particular, to a clearance monitor for a forage harvester cutting machine.
With current production forage harvester machines, the blade-shearbar clearance and blade sharpness critically influence the overall quality and efficiency of the forage cutting operation. For example, oversharpening results in excessive repair costs while undersharpening results in wasted fuel due to high power requirements, poorly cut forage and excessve strain on power train and cutterhead components. At present, operators must rely upon their senses (such as hearing) guided by experience in order to make judgements about the status of the blade-shearbar clearance to determine when blade sharpening and shearbar repositioning is required. It is difficult to achieve optimum operation of the forage harvester while relying on fallible human senses. An alternative is to periodically sharpen the blades and reposition the shearbar according to a set schedule. This alternative may result in corrective action being taken either before or after such action is strictly necessary, with resulting inefficiencies. Furthermore, when adjusting the shearbar blade clearance after blade sharpening, operators have been required to advance the shearbar toward the reverse rotating blades until a "clicking" sound is perceived, then to back the shearbar back away from the blades by a prescribed amount. Such an adjustment also is only as effective as the operator's judgment, experience and sense of hearing. Accordingly, it would be desirable to provide a means for monitoring blade-shearbar clearance which does not rely upon human senses, judgment and experience.
Variable capacitance sensing techniques have been used to measure the clearance in cutting tools. However, such sensors require that a relative potential be applied between the relatively movable cutting parts which necessitates electrically isolating those parts from each other. Furthermore, such capacitive sensors could yield misleading readings due to changes in the dialectric constant of the material being cut, such as would be caused by changes in the type of or moisture content of the forage materials. Eddy current sensing devices have also been used to measure the distance between a stationary sensor and a moving metal target object. However, such devices are expensive because they require the projection of a low level inductive field in front of the device and the sensing of eddy currents induced in the target object. Therefore, it would also be desirable to provide a clearance detector which utilizes an inexpensive distance measuring device which is relatively insensitive to dialectric variations in the material to be cut.